The present invention is directed to a fluid flowmeter for sensing the flow rate of a fluid, and in particular to a fluid flowmeter having a Hall Effect sensor including an internal magnet adapted to sense movement of a metal pole piece located in an impeller.
Prior fluid flowmeters included multiple magnets that were located in the fluid passageway of the flowmeter and that were passed in front of a Hall Effect sensor to detect the flow rate of the fluid. Use of multiple magnets increases the cost of manufacturing the flowmeter, creates an unnecessarily large magnetic field which potentially interferes with other instrumentation, and makes removal and replacement of the magnet difficult. The present invention locates the magnet outside of the fluid passageway and eliminates the use of multiple magnets thereby lowering the cost of manufacture and providing a reduction in the magnetic field created by the flowmeter.
A flowmeter for sensing fluid flow. The flowmeter includes a housing having a wall, a first port, a second port, a chamber in fluid communication with the first port and the second port, and a fluid passageway extending from the first port to the second port through the chamber. The flowmeter also includes a non-magnetized impeller located within the chamber of the housing that is rotatable about an axis. The impeller includes a shaft having a cylindrical bore, a base attached to the shaft, and one or more blades attached to the shaft and extending radially outwardly from the shaft. The base of the impeller includes a carrier member. A non-magnetized metal pole piece is enclosed within the carrier member that includes two arms extending radially outwardly from the central axis of the shaft. A cap having a spindle is attached to the housing. The bore of the shaft of the impeller is adapted to receive the spindle such that the impeller is rotatably mounted on the spindle and is rotatable with respect to the spindle. A first end of the spindle is attached to the cap and the second end of the spindle is adapted to be located in a recess formed in the wall of the housing. The flowmeter also includes a Hall Effect sensor having an internal magnet. The Hall Effect sensor and the magnet are located outside of the fluid passageway with the Hall Effect sensor located within an exterior pocket formed in the wall of the housing. The wall of the housing separates the Hall Effect sensor and the magnet from the fluid passageway. Fluid flowing through the fluid passageway rotates the impeller and the pole piece about the axis of the impeller and the magnetic field generated by the magnet enables the Hall Effect sensor to sense the speed of rotation of the impeller and to thereby sense the rate of fluid flow through the fluid passageway.